Organic EL light-emitting device and production method thereof

ABSTRACT

There is provided a method of producing an organic EL light-emitting device which enables prevention of crosstalk between adjacent pixels of the same color. Provided is a method of producing an organic EL light-emitting device which has banks provided in a row direction and in a column direction, and a plurality of organic EL light-emitting portions isolated from each other by the banks. The method includes the steps of forming banks such that a height of a bank portion of a row direction and a height of a bank portion of a column direction are different from each other; and applying an organic EL material in a continuous manner along the bank portion which is higher of the bank portion of the row direction and the bank portion of the column direction, between the banks of the higher bank portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/548,846, filed Oct. 12, 2006 now U.S. Pat. No. 7,503,823, whichclaims priority of Japanese Patent Application No. 2005-358619, filed onDec. 13, 2005 and Japanese Patent Application No. 2006-271542, filed onOct. 3, 2006 under 35 U.S.C. §119. The contents of all of theaforementioned applications are hereby incorporated by reference hereinin their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescence(hereinafter, simply referred to as “EL”) light-emitting deviceutilizing EL of an organic compound material which emits light whencurrent is injected therein, and a production method thereof. Moreparticularly, the present invention relates to an organic ELlight-emitting device having banks for isolating pixels, and aproduction method thereof.

2. Description of the Related Art

In the production of the organic EL light-emitting device, which ispromising for a large-area display, an organic EL light-emittingmaterial has been applied to a large-size substrate in an attempt toreduce the production cost.

Japanese Patent Application Laid-Open No. H10-153967 discloses a methodof fabricating a light-emitting device using an inkjet system, which isa typical method for applying such a material. The method is describedbelow.

As shown in FIG. 8, transparent anode electrodes 82 made of indium tinoxide (hereinafter referred to as “ITO”) or the like are fabricated on atransparent substrate 81 using photolithography. Then, “banks” 83 (ofpolyimide, for example) for pixel isolation having high electricalinsulation properties are formed between the transparent electrodes 82using photolithography. Then, layers, such as a hole injection layer anda light-emitting layer, are formed in the mentioned order in each of thepixels, by dropping and coating with the aid of an inkjet system. Atthis time, the height of each of the “banks” needs to be sufficientlylarge with respect to the thickness of the organic EL layer. The purposeof this is to prevent such a phenomenon that when an organic EL materialis ejected from a nozzle 85 of an inkjet system (not shown) and arrivesat each of the pixels, a part of the material bounces from the substrateto be scattered to the periphery of the pixel and be mixed into anadjacent organic EL material across the bank. In the figure, referencecharacters 84 a, 84 b, and 84 c denote organic EL materials for red,blue, and green, respectively. Further, as shown in FIGS. 9A and 9B,banks 91 of a column direction and banks 92 of a row direction areformed into shapes for surrounding each of the pixels for accomplishmentof isolation between the pixels. In the figures, reference characters 93a, 93 b, and 93 c denote organic EL materials for red, blue, and green,respectively. Thus, as disclosed in Japanese Patent ApplicationLaid-Open No. H10-153967, in the case of the inkjet system, the heightsof the “banks” are substantially identical at any location (i.e., h5=h6in FIG. 9B).

Next, Japanese Patent Application Laid-Open No. 2002-075640 discloses amethod of fabricating a light-emitting device using the so-called nozzleprinting, which is another method for applying an organic EL material.The method is described below.

As shown in FIG. 6, after forming transparent anode electrodes 62 madeof ITO on a transparent substrate 61 by using photolithography, “banks”63 suitable for nozzle printing and for pixel isolation formed in astriped pattern (corresponding to banks 73 of a column direction in FIG.7) by photolithography. In this case, the heights of the banks need tobe sufficiently large to such an extent that required amounts of appliedinks (organic EL materials 64 a, 64 b, and 64 c for red, blue, andgreen, respectively) do not get over the banks 63 and to also besubstantially identical at any location (see FIG. 6). A nozzle 65 ismoved at a high speed along the striped banks 73. The characteristic ofthe nozzle printing is that the viscosity and pressure of a solution(for example, organic EL material 64 for red) are adjusted, so that arequired amount of the solution can be dropped into a groove portionbetween banks with one ejection. That is, by continuously dropping theorganic EL material in the groove (without any break, as in the case ofdrawing a continuous line with a single stroke of an ink pen), theproblem of “contamination of ink (color mixing) due to bouncing back ofliquid droplet across bank” in the ink jet system is overcome. Thetechnique of dropping an organic EL material in a groove in a continuousmanner (without any break, as in the case of drawing a continuous linewith a single stroke of an ink pen) is hereinafter referred to as“nozzle printing”.

However, as disclosed in Japanese Patent Application Laid-Open No.2002-075640, in the case of the nozzle printing, because the “banks” 73are provided in the striped pattern (see FIG. 7), there is no physicalisolation between pixels of the same color disposed in a direction 76 inwhich the relative positional relationship between a nozzle 75 and aformed film-shaped member changes (hereinafter referred to as “scanningdirection”). Accordingly, there is posed the problem of crosstalkbetween adjacent pixels of the same color. The crosstalk is attributableto the transmission of light emitted by a light-emitting layer betweenadjacent pixels of the same color through organic compound layers, suchas the light-emitting layer, a hole-transporting layer, and anelectron-transporting layer.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodof producing an organic EL light-emitting device, which is capable ofpreventing crosstalk between adjacent pixels of the same color.

The present invention provides a method of producing an organic ELlight-emitting device having banks provided in a row direction and in acolumn direction, and a plurality of organic EL light-emitting portionsisolated from each other by the banks, the method comprising the stepsof: forming banks such that a height of a bank portion of a rowdirection and a height of a bank portion of a column direction aredifferent from each other; and applying an organic EL material in acontinuous manner along the bank portion which is higher of the bankportion of the row direction and the bank portion of the columndirection, between the banks of the higher bank portion.

Further, the present invention also provides an organic ELlight-emitting device which comprises banks provided in a row directionand in a column direction, and a plurality of organic EL light-emittingportions isolated from each other by the banks, wherein a height of abank portion of the row direction and a height of a bank portion of thecolumn direction are different from each other.

According to the present invention, an organic EL material is applied bythe nozzle printing in a state in which low banks (banks of a rowdirection) are formed in a direction which intersects the scanningdirection, whereby crosstalk between adjacent pixels of the same colorcan be prevented.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view illustrating an organic ELlight-emitting device (Embodiment 1, Example 1) of the presentinvention, and FIGS. 1B and 1C are cross-sectional views taken alonglines 1B-1B and 1C-1C in FIG. 1A, respectively.

FIG. 2A is a schematic plan view illustrating the organic ELlight-emitting device (Embodiment 1, Example 1) of the presentinvention, and FIGS. 2B and 2C are cross-sectional views taken alonglines 2B-2B and 2C-2C in FIG. 2A, respectively.

FIG. 3A is a schematic plan view illustrating an organic ELlight-emitting device (Embodiment 2, Example 2) of the presentinvention, and FIGS. 3B and 3C are cross-sectional views taken alonglines 3B-3B and 3C-3C in FIG. 3A, respectively.

FIG. 4A is a schematic plan view illustrating the organic ELlight-emitting device (Embodiment 2, Example 2) of the presentinvention, and FIGS. 4B and 4C are cross-sectional views taken alonglines 4B-4B and 4C-4C in FIG. 4A, respectively.

FIGS. 5A and 5B are schematic plan views illustrating the shapes ofmasks A and B used in forming banks of an organic EL light-emittingdevice of the present invention, respectively.

FIG. 6 is a schematic cross-sectional view illustrating formation of anorganic EL device by nozzle printing.

FIG. 7 is a schematic plan view illustrating formation of an organic ELdevice by nozzle printing.

FIG. 8 is a schematic cross-sectional view illustrating formation of anorganic EL device using an ink jet system.

FIG. 9A is a schematic plan view illustrating formation of an organic ELdevice using an inkjet system, and FIG. 9B is a cross-sectional viewstaken along line 9B-9B in FIG. 9A.

FIG. 10 is a schematic cross-sectional view illustrating formation of anorganic EL device with a second electrode (cathode) continuouslyextending over a plurality of light-emitting portions which are adjacentto each other.

DESCRIPTION OF THE EMBODIMENTS

The present invention provides an organic EL light-emitting device whichis formed by applying an organic EL material by nozzle printing, and aproduction method thereof. In particular, the present invention providesan organic EL light-emitting device which also prevents crosstalkbetween same-color pixels of an organic EL material.

Specifically, the method of the present invention is for producing anorganic EL light-emitting device having banks provided in a rowdirection and in a column direction, and a plurality of organic ELlight-emitting portions isolated from each other by the banks. Further,the production method of the present invention comprises the steps offorming banks such that a height of a bank portion of a row directionand a height of a bank portion of a column direction are different fromeach other; and applying an organic EL material in a continuous manneralong the bank portion which is higher of the bank portion of the rowdirection and the bank portion of the column direction, between thebanks of the higher bank portion.

Further, the organic EL light-emitting device of the present inventioncomprises banks provided in a row direction and in a column direction,and a plurality of organic EL light-emitting portions isolated from eachother by the banks, wherein a height of a bank portion of the rowdirection and a height of a bank portion of the column direction aredifferent from each other.

The banks are provided between the plurality of organic ELlight-emitting portions. In other words, the banks comprise a bankportion provided in a row direction and a bank portion provided in acolumn direction. When the light-emitting device has the organic ELlight-emitting portions in a plurality of rows and a plurality ofcolumns, the bank portions are also provided in a plurality of lines inboth the row and the column directions. In the present invention, theheight of the bank portion provided in the row direction is differentfrom that of the bank portion provided in the column direction. Theheight at a location where the bank portion of the row direction and thebank portion of the column direction intersect each other is defined asthe height of the bank portion which is higher of the both bankportions. In this regard, the term “height” herein employed refers tothe distance from a surface of an electrode provided under the organicEL layer to a position which is most distant from the electrode.

The banks are formed so as to be provided between the plurality oforganic EL light-emitting portions, in other words, so as to have thebank portions in the row and the column directions. The formation of thebanks is carried out prior to the application of the organic ELmaterials. This is because the banks eventually bank the applied organicEL materials.

The organic EL light-emitting portions each have a pair of electrodesand an organic compound layer disposed therebetween. Thus, holesinjected from the anode and electrons injected from the cathode arerecombined in the organic compound layer, and when excited moleculesreturn to a ground state, light is emitted. The organic compound layercontains at least a light-emitting layer, and may additionally containother layers, such as a hole-transporting layer, anelectron-transporting layer, a hole injection layer, or an electroninjection layer.

The organic EL light-emitting portion is formed in plurality while beingisolated from each other in the row and the column directions. Theorganic compound layers are each formed by continuous application of anorganic EL material while being isolated from each other by the banks.The term “continuous application” herein employed refers, in particular,to applying an organic EL material linearly without any break. In thiscase, in order that a uniform film can be formed at the respectiveorganic EL light-emitting portions, it is preferable that the relativepositional relationship between a nozzle and a formed film-shaped memberchanges at a constant rate while ejecting a given amount of organic ELmaterial from a nozzle. The terms “row direction” and “column direction”herein employed do not refer to “horizontal direction” and “verticaldirection”, respectively, in a display surface when the organic ELlight-emitting device of the present invention is applied to a displaydevice. However, description will be made below with the horizontaldirection in the drawing being the “row direction” and with the verticaldirection therein being the “column direction”, for convenience of thedescription. Incidentally, it is to be noted that the “row direction”and the “column direction” do not necessarily need to intersect eachother perpendicularly.

Formation of the organic EL light-emitting portions is carried out, byapplying organic EL materials, in a state in which not only the bankportions parallel to the scanning direction (direction in which therelative positional relationship between the nozzle and a formedfilm-shaped member changes) but also the bank portions intersecting thescanning direction have been formed. Further, the latter bank portionsare formed so as to have a smaller height than the former bank portionsto thereby realize physical isolation of the same ink (organic ELmaterial). In order to isolate inks of different colors (e.g., organicEL materials 64 a and 64 b, and organic EL materials 64 b and 64 c) fromeach other and to prevent color mixing, the heights of the bank portionsparallel to the scanning direction need to be sufficiently larger thanthe thicknesses of films of applied ink. However, because it issufficient for the bank portions intersecting with the scanningdirection to provide isolation of a same-color ink (organic ELmaterial), the heights of those bank portions may be just larger thanthe final thicknesses of films of the organic EL material. Further, inorder to prevent the breakage of the continuity of a coating liquid fromthe nozzle, the lower the bank portions which intersect the scanningdirection, the better.

When applying the organic EL materials, in the case of using a differentorganic EL material for each organic EL light-emitting portion of adifferent emission color (e.g., the organic EL materials 64 a and 64 b,and the organic EL materials 64 b and 64 c), the organic ELlight-emitting portions of the same color are disposed linearly in thescanning direction. Therefore, the pixel arrangement of the organic ELlight-emitting device obtained according to the production method of thepresent invention is the so-called stripe arrangement in which organicEL light-emitting portions of plural colors are periodically arrangedlinearly.

Hereinafter, embodiments of the present invention are described withreference to the attached drawings.

(Embodiment 1)

FIGS. 1A, 1B, and 1C are schematic views showing banks of an organic ELlight-emitting device according to Embodiment 1 of the presentinvention. FIGS. 2A, 2B, and 2C are schematic views showing a state inwhich an organic compound layer is provided in each of areas defined bythe banks of the organic EL light-emitting device, according toEmbodiment 1 of the present invention. FIGS. 1A and 2A are plan views,and FIGS. 1B, 1C, 2B and 2C are cross-sectional views. In the organic ELlight-emitting device of the present invention, electrodes are providedunder the organic compound layer (back side of the drawing) and on theorganic compound layer (front side of the drawing). However, in FIGS. 1Ato 1C and FIGS. 2A to 2C, the devices are represented schematically withthe electrodes being omitted for convenience of presentation. Theorganic EL light-emitting device of the present invention may be of theso-called passive matrix type in which striped electrodes intersect eachother. Alternatively, the organic EL light-emitting device of thepresent invention may be of the so-called active matrix type in whichone of the electrodes is defined for each organic EL light-emittingportion, and the other of the electrodes is provided so as to extendover the organic EL light-emitting portions.

In FIGS. 1A, 1B, and 1C, reference numeral 11 denotes bank portions of acolumn direction, and reference numeral 12 denotes bank portions of arow direction. In FIGS. 2A, 2B, and 2C, reference numeral 21 denotesbank portions of a column direction, reference numeral 22 denotes bankportions of a row direction, and reference characters 23 a, 23 b, and 23c denote organic EL layers for red, blue, and green, respectively.

As shown in FIGS. 1A to 1C and FIGS. 2A to 2C, Embodiment 1 of thepresent invention is an organic EL light-emitting device formed byapplying organic EL materials by nozzle printing, and accordingly, bankportions parallel to the scanning direction are formed. Further,additional bank portions are also formed in a direction which intersectswith the scanning direction. At this time, when the height of the bankportions parallel to the scanning direction is represented by “h1”, andthe height of the bank portions formed in the direction intersectingwith the scanning direction is represented by “h2”, the relationship ofh1>h2 is satisfied. It is sufficient that the height “h2” of the bankportions formed in the direction intersecting the scanning directionprovides isolation of an ink between the pixels in the scanningdirection, and the mixing of the ink between adjacent pixels in thescanning direction causes no problem (because the same ink is used).Accordingly, the smaller the “h2”, the better. However, the minimumvalue may only have to be equal to or more than the total thicknessincluding the thicknesses of the organic EL layers and a cathodeelectrode. Specifically, the heights may, respectively, be as follows.1 μm<h1<10 μm; 0.1 μm<h2<2 μm

The material of the banks may only have high electrical insulatingproperties. Preferable examples of the material include resins such aspolyimide resin, polyester resin, styrene-acrylic copolymer resin,acrylic resin or the like; those materials obtained by adding anadditive to the foregoing resin; and SiO₂. Further, it is alsopreferable that the surface of the bank is water-repellent, and that theinside of the bank, i.e., the region defined by the banks to serve asthe organic EL light-emitting portion is hydrophilic so that ink(organic EL material) can be fixed thereto. For example, in the casewhere the bank is made of polyimide resin, after making the inside ofthe groove thereof hydrophilic by O₂ plasma treatment, the bank can bemade water-repellent by CF₄ plasma treatment.

The method of making the heights of the banks different from each otherbetween the column direction and the row direction is not particularlylimited. However, when photolithography is used, two types of photomasksare provided, while a bank material is applied (or deposited) first tothe entire surface, followed by further application of a photoresistonto the entire surface. Subsequently, the resultant is subjected toexposure for development for a predetermined period of time using aphotomask masking those portions corresponding to the bank portionsparallel to the nozzle scanning direction (bank portions of columndirection), and then subjected to etching using the remaining resist asa mask for a predetermined period of time. Further, a photoresist isapplied thereon, which is then subjected to exposure for a predeterminedperiod of time for development using a photomask masking those portionscorresponding to both of the bank portions parallel to the scanningdirection (bank portions of column direction) and the bank portionsintersecting the scanning direction (bank portions in row direction).Thereafter, etching is performed using the remaining resist as a maskfor a predetermined period of time. As a result, the height of the bankportions of the row direction can be fabricated to be smaller than theheight of the bank portions of the column direction (for details, seeExample 1).

In another approach, a photomask is provided in which the width of eachof those portions corresponding to the bank portions of the columndirection is made larger than the width of each of those portionscorresponding to the bank portions of the row direction. The resistremaining as a result of exposure-development using the mask has thefollowing relation: (the width of the bank portion of the columndirection)>(the width of the bank portion of the row direction).

Subsequently, when the bank material is etched using the remainingresist structure as a mask, polyimide banks having the followingrelation can be fabricated: (the width of the bank portion of the columndirection)>(the width of the bank portion of the row direction).

The height of the banks at this moment is uniform at any position. Next,the surface of the device is heated to such a temperature as to softenthe polyimide material, whereby the polyimide banks are softened. As aresult, in the context of a difference in heat capacity, the height ofthe bank portions having the smaller width becomes smaller than that ofthe bank portions having the larger width. In this way, a device havingthe following relation can be obtained: (the height of the bank portionof the column direction)>(the height of the bank portion of the rowdirection).

Other approaches, such as those utilizing a change in transmittance of aphotomask, or utilizing a phase-shift mask may also be used to achievethe same result.

(Embodiment 2)

FIGS. 3A, 3B, and 3C are schematic views showing banks of an organic ELlight-emitting device according to Embodiment 2 of the presentinvention. FIGS. 4A, 4B, and 4C are schematic views showing a state inwhich an organic compound layer is provided in each of areas defined bythe banks of the organic EL light-emitting device, according toEmbodiment 2 of the present invention. FIGS. 3A and 4A are plan views,and FIGS. 3B, 3C, 4B and 4C are cross-sectional views. In the organic ELlight-emitting device of the present invention, electrodes are providedunder the organic compound layer (back side of the drawing) and on theorganic compound layer (front side of the drawing). However, in FIGS. 3Ato 3C and FIGS. 4A to 4C, the devices are represented schematically withthe electrodes being omitted for convenience of presentation.

In FIGS. 3A, 3B, and 3C, reference numeral 31 denotes bank portions of acolumn direction, and reference numeral 32 denotes bank portions of arow direction. In FIGS. 4A, 4B, and 4C, reference numeral 41 denotesbank portions of a column direction, reference numeral 42 denotes bankportions of a row direction, and reference characters 43 a, 43 b, and 43c denote organic EL layers for red, blue, and green, respectively.

In the organic EL light-emitting device according to Embodiment 2 of thepresent invention, which is formed by applying organic EL materials bynozzle printing, bank portions with a smaller height each have inclinedsurfaces in the longitudinal direction, in addition to the configurationof the device of Embodiment 1. In other words, the bank portionsintersecting the scanning direction each have inclined surfaces in thelongitudinal direction of the bank portions parallel to the scanningdirection.

The term “having inclined surfaces” herein employed means, for example,that each of the banks has a triangular cross section as shown by thecross-sectional view of FIG. 3C which is taken along line 3C-3C in thescanning direction. In other words, where the height of the banks of thecolumn direction is represented by “h3” and the height of the banks ofthe row direction is represented by “h4” as shown in FIG. 3B, therelation of h3≧h4 is satisfied, and further, as shown in FIG. 3C, thebanks of the row direction each have a triangular cross section and eachhave no plane parallel to the bottom. In the present invention, thereason why the height “h4” of the bank portions of the row direction ismade equal to or smaller than the height “h3” of the bank portions ofthe column direction is that the bank portions of the row direction areprovided in order to give isolation of the ink of the same color andtherefore that the same-color ink poses no problem of color mixingbetween adjacent pixels.

Accordingly, the smaller the “h4”, the better. However, the minimumvalue may only have to be equal to or more than the total thicknessincluding the thicknesses of the organic EL layers and a cathodeelectrode. Specifically, the heights may, respectively, be as follows.1 μm<h3<10 μm; 0.1 μm<h4<2 μm

Further, for the purpose of accelerating isolation (or separation) of anink (of the same color) into pixels in the column direction, the bankportions are each made to have a triangular cross section consisting ofonly inclined portions such as shown in FIG. 3C. No formation of a flatportion at the top of the bank portions can prevent the ink fromremaining at the bank portions (conventional banks have a trapezoidalshape).

The technique of imparting a bank portion with a shape whose crosssection is triangle is not particularly limited, but such banks may befabricated by selecting resist materials or exposure conditions(defocused condition, for example). Alternatively, after forming banksof different widths, the banks may be deformed by etching or heattreatment. Alternatively, utilization of a change in transmittance of aphotomask, or utilization of a phase-shift mask, for example, mayachieve the same result.

As described above, according to the organic EL light-emitting device ofthe present invention, such measures are taken as making the height ofthe bank portions of a row direction smaller than that of theconventional bank portions of a column direction, or providing astructure in which the bank portions of the row direction have inclinedsurfaces, so that the continuity of dropping of a coating liquid, whichis the characteristic of nozzle printing, is prevented from beingimpaired.

The method of fabricating bank portions of a row direction is achievedby only adding steps of the same level as those employed in theconventional fabrication method of bank portions of a column direction,without requiring particular steps or apparatuses, thereby avoidingincrease of the production cost.

As described above, according to the present invention, completeisolation of an organic EL material into respective pixels can beensured even when using nozzle printing. Accordingly, the presentinvention enables use of the coating process of nozzle printing toprovide an organic EL light-emitting device. The organic ELlight-emitting device of the present invention is applicable to displayportions of, for example, digital cameras, television receivers,cellular phones, and PC monitors. Application of the organic ELlight-emitting device of the present invention to such display portionscan provide electronic devices of high display quality hardly causingcrosstalk.

EXAMPLES

The present invention is described below referring to specific examples.However, the present invention is not limited to the examples.

Example 1

In the present example, an organic EL light-emitting device according toEmbodiment 1 was produced.

First, a method of producing an organic EL light-emitting device usingthe conventional nozzle printing is described below with reference toFIG. 6 (cross sectional view) and FIG. 7 (plan view), each of whichillustrates organic EL light-emitting portions of the organic ELlight-emitting device.

In the conventional nozzle printing process, organic EL layers, such asa hole injection layer and a light-emitting layer (red 64 a, blue 64 b,and green 64 c) are formed between banks 63 by coating using a nozzle65. At this time, the technique of continuously dropping a liquid ink(organic EL material, for example, 64) is adopted, so that the problemassociated with the use of the conventional ink jet system such as shownin FIG. 8 that droplets of ink (organic EL material, for example, 84) goacross the banks to be mixed into adjacent pixels is resolved.

However, as shown in FIG. 7, in the conventional nozzle printingprocess, banks 73 alone have been formed, which are parallel to thescanning direction 76, so that color separation of the organic EL layers74 a, 74 b, and 74 c has been performed.

In the present example, as shown in FIG. 1A, in addition to theconventional banks 11 parallel to the scanning direction (hereinafterreferred to as “banks of a column direction”), banks 12 were also formedin a direction perpendicular to the scanning direction (hereinafterreferred to as “banks of a row direction”). Here, as shown in FIG. 1B,when the height of the bank portions of the column direction isrepresented by “h1”, and the height of the bank portions of the rowdirection is represented by “h2”, the relationship of h1>h2 is ensuredto be satisfied.

The banks were formed by using conventional photolithography and etchingtechniques. ITO was provided and patterned on a transparent substrate61. Then, a 2 μm thick film of polyimide as the material of the banks 63was formed entirely on the top surface thereof, followed by theapplication of a positive photoresist material (not shown) entirely onthe surface thereof in a thickness of 2 μm.

Subsequently, the resultant was exposed using a photomask A shown inFIG. 5A. The photomask A has a mask portion 51 which does not transmitlight and corresponds to the bank portions of the column direction. Aportion of the resist not protected by the photomask A was dissolved andremoved by development carried out after the exposure. Then, thepolyimide was etched with the remaining resist material structure beingused as a mask. At this time, the etched portion was ensured to have adepth of 0.5 μm.

Then, the resultant was exposed using a photomask B shown in FIG. 5B.With the photomask B, light is shielded at a portion 52 whichcorresponds to the bank portions of both the column and the rowdirections. A portion of the resist not protected by the photomask B wasdissolved and removed by development carried out after the exposure.Then, the polyimide was etched with the remaining resist materialstructure being used as a mask. The depth of the portion etched by thissecond etching was 1.5 μm.

Thus, the polyimide banks that were protected by both of the photomasksA and B and remained became the bank portions 11 of the columndirection, with the height “h1” being 2 μm. On the other hand, theportion which was exposed by the photomask A but was not exposed by thephotomask B became the bank portions 12 of the row direction, with theheight “h2” being 1.5 μm. Further, the bank portions 11 of the columndirection had a width of 20 μm and a pitch of 180 μm. The bank portions12 of the row direction had a width of 20 μm and a pitch of 250 μm.

In this way, the structure having the polyimide banks as shown in FIGS.1A and 1B was obtained.

Subsequently, O₂ plasma treatment was performed from above the topsurface of the structure having the polyimide banks to make the entiresurface hydrophilic. Then, only the polyimide bank portions aresubjected to CF₄ plasma treatment to make only the bank portionswater-repellent. By performing these procedures, there is obtained theeffect that an organic EL material, which is in a form of a solution, islikely to be repelled by the bank portions and is likely to stay withinthe banks of the pixels (i.e. regions defined by the banks and servingas the organic EL light-emitting portions).

After that, the structure was used and subjected to stack coating withthe organic EL materials 64 a, 64 b, and 64 c using the conventionalnozzle printing process such as shown in FIG. 6. After the organicsolvent was dried, it was observed that as shown in FIGS. 2A to 2C,isolation of same-color ink was accomplished in the column direction foreach of the organic EL layers 23 a, 23 b, and 23 c, owing to the bankportions 22 of the row direction. Further, as shown in FIG. 10, after anAl electrode 94 was formed as a cathode electrode entirely on the topsurface of each of the organic EL layers to perform encapsulation, thecharacteristics of the organic EL light-emitting device were evaluated,with the result that crosstalk was scarcely observed between adjacentpixels.

As described above, according to the present invention, provision of thelow bank portions 22 in the row direction enables physical isolationbetween adjacent pixels in the scanning direction without impairing thecontinuity of application of ink of the nozzle printing. It wasconfirmed to be sufficient for the present invention that the bankportions 22 of the row direction had a height of at least 0.5 μm (whilethe bank portions of the column direction required a height of 2 μm ormore).

Example 2

FIGS. 3A to 3C and FIGS. 4A to 4C show the organic EL light-emittingdevice according to Embodiment 2 of the present invention. FIGS. 3A and4A are plan views, and FIGS. 3B, 3C, 4B and 4C are cross-sectionalviews.

In the present example, as shown in FIG. 3A, the bank portions 32 of therow direction were formed in addition to the conventional bank portions31 of the column direction parallel to the nozzle scanning direction.Here, as shown in FIG. 3B, when the height of the bank portions 31 ofthe column direction is represented by “h3”, and the height of the bankportions 32 of the row direction is represented by “h4”, therelationship of h3>h4 is ensured to be satisfied. Further, as shown inFIG. 3C, the bank portions 32 of the row direction was each formed so asto have inclined surfaces, i.e., so as to have a triangular crosssection and have no plane parallel to the bottom.

A method of fabricating banks and the shapes of the banks are describedin detail below.

Conventional photolithography and etching processes were used for thefabrication of the banks.

Similarly as in Example 1, after forming an ITO 62 film, a polyimidefilm and a photoresist film on a transparent substrate 61,exposure/development was performed using the photomask B shown in FIG.5B, followed by etching of the polyimide. The shapes of polyimide banksremaining after the etching were such that the width of the bank portion31 of the column direction was 20 μm with the pitch thereof being 180μm, the width of the bank portion 32 of the row direction was 5 μm withthe pitch thereof being 200 μm, and the heights of the banks were all 3μm. Then, appropriate conditions were selected to perform dry etchingwith respect to the surface of the light-emitting device. Generally,when dry etching is performed with respect to the surface of a surfacestructure (structure having unevenness in a surface thereof), plasma isconcentrated to protruded portions (polarized portions) of the structureto deform the structure. By utilizing this phenomenon, in the presentexample, it was possible to accelerate deformation of the bank portionshaving the smaller width. Specifically, the bank portions 32 of the rowdirection after the dry etching each had a width of 5 μm and a pitch of200 μm and each presented a triangular cross section such as shown inFIG. 3C with a height h4 of 1 μm. On the other hand, the shapes of thebank portions 31 of the row direction was hardly changed by the dryetching, and had a width of 20 μm, a pitch of 180 μm, and a height of 3μm.

In this way, a structure having the banks such as shown in FIGS. 3A to3C was obtained, and the surface shape thereof was such that therelation of h3>h4 was satisfied and the bank portions of the rowdirection presented a shape having no plane parallel to the bottom,i.e., a triangular cross section.

Subsequently, similarly as in Example 1, O₂ plasma treatment wasperformed from above the top surface of the structure having thepolyimide banks to make the entire surface hydrophilic. Then, only thepolyimide bank portions are subjected to CF₄ plasma treatment to makeonly the bank portions water-repellent. These procedures are performedin order to obtain the effect that an organic EL material, which is in aform of a solution, is likely to be repelled by the bank portions and islikely to stay within the banks of the pixels (i.e. regions defined bythe banks and serving as the organic EL light-emitting portions).

After that, the structure was subjected to stack coating with theorganic EL materials 64 a, 64 b, and 64 c using the conventional nozzleprinting process such as shown in FIG. 6. After the organic solvent wasdried, it was observed that as shown in FIGS. 4A to 4C, isolation ofsame-color ink was accomplished in the column direction for each of theorganic EL layers 43 a, 43 b, and 43 c, owing to the bank portions 42 ofthe row direction. Further, as shown in FIG. 10, after an A1 electrodewas formed as a cathode electrode 94 entirely on the top surface of eachof the organic EL layers 43 a, 43 b, and 43 c to perform encapsulation,the characteristics of the organic EL light-emitting device wereevaluated, with the result that crosstalk was scarcely observed betweenadjacent pixels.

As described above, according to the present invention, provision of thelow bank portions 42 in the row direction enables physical isolationbetween adjacent pixels in the scanning direction without impairing thecontinuity of application of ink of the nozzle printing. It wasconfirmed to be sufficient for the present invention that the bankportions 42 of the row direction had a height of at least 1 μm (whilethe bank portions of the column direction required a height of 3 μm ormore).

Comparative Example 1

An organic EL light-emitting device was produced by following the sameprocedure as in Example 1 with the exception that no bank portion of arow direction was formed, and that the mask used for thephotolithography was only the one shown in FIG. 5A. According to thepresent comparative example, the organic EL device formed by the nozzleprinting process had the structure shown in FIG. 7.

Next, similarly as in Example 1, the characteristics of the thusproduced light-emitting device were evaluated, with the result thatcrosstalk was generated between adjacent pixels made of light-emittinglayers of the same color and that the luminance was lower.

In other words, in the organic EL light-emitting device of the presentcomparative example, the problem of generation of crosstalk betweensame-color light-emitting layers in the column direction was posedbecause no bank of a row direction was present.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims priority from Japanese Patent application No.2005-358619 filed on Dec. 13, 2005, 2006-271542 filed on Oct. 3, 2006,which are hereby incorporated by reference herein.

1. A method of producing an active matrix organic light-emitting devicecomprising a plurality of organic light-emitting portions, the methodcomprising: forming a plurality of first electrodes corresponding to theplurality of organic light-emitting portions; forming banks forisolating the plurality of organic light-emitting portions from eachother, the banks comprising a bank portion of a row direction, a bankportion of a column direction, and a bank portion at an intersection ofthe row direction and the column direction, and the bank portion of thecolumn direction and the bank portion at the intersection are higherthan the bank portion of the row direction; applying an organic ELmaterial to the organic light-emitting portions in a continuous manneralong the column direction; drying the applied organic EL material toform an organic El layer; forming a second electrode on the organic ELlayer, wherein a height of a surface of the second electrode in theorganic light-emitting portion is smaller than or equal to a height of asurface of the bank portion of the row direction, and wherein the secondelectrode is continuously formed so as to continuously extend over theplurality of light-emitting portions which are adjacent to each other inthe row direction and in the column direction.
 2. The method ofproducing an active matrix organic light-emitting device according toclaim 1, wherein the step of forming banks comprises: providing a bankmaterial on a plurality of first electrodes so as to continuously extendover the plurality of organic light-emitting portions which are adjacentto each other in the row direction and in the column direction; etchingthe bank material provided on the plurality of first electrodes andbetween the first electrodes, in the row direction; and further etchingthe bank material provided on the plurality of first electrodes toexpose the first electrodes.
 3. The method of producing an active matrixorganic light-emitting device according to claim 1, wherein the heightof the bank portion of the column direction is more than 1 μm and lessthan 10 μm, and the height of the bank portion of the row direction ismore than 0.1 μm and less than 2 μm.